Tunnel kiln



Sept 8, 1936.

J. J. SCHARF ET AL TUNNEL KILN Filed Aug 7, 1934 4 Sheets-Sheet 1 m pm.VB 3M w c E? 3% d A w? a E um M .WL

l|| IIIIIFIIIIIFI l kllllllll HMHHHEHWNMQ Sept; 8, 1936.

J. J. SCHARF ET AL TUNNEL KILN Filed. Aug 7, 1934 4 Sheets-Sheet 43m$entors doH/v u 6CHHPF. WILL/AM HASSELB/ICH.

LUTHE? yreommce f Ml amm'e i atented Sept. 8, 1936 um'reo STATES PATENToFFieE TUNNEL KILN John J. Scharf, William Hasselbach, and Luther T.Strommer, Toledo, Ohio, assignors to Libbey-Owens-Ford Glass Company,Toledo, Ohio, a corporation of Ohio Application August 7, 1934, SerialNo. 738,774 19 Claims. (01. 25-142) The present invention relates toimprovements means and utilizing it to assist in heating up the intunnel kiln. auxiliary heating zone of the said primary tunnel While thetunnel kiln herein provided is not structure, the said heated air beingsubsequently restricted to any specific use,- it is of utility whencaused to flow longitudinally through the primary employed for thefiring or arching of glass melttunnel structure and constituting the airsupply ing pots. These pots are formed of a refractory for the gasburners used in heating the high material and, after firing, are adaptedto be temperature or firing zone. 1 placed in a glass melting furnaceand tohave Other objects and advantages of the invention molten glassproduced therein. In view of the will become more apparent during thecourse of exceedingly high temperatures to which these the followingdescription when taken in connec- 1( pots are subjected during themelting of the glass, tion with the accompanying drawings.

it is essential that the firing treatment thereof In the drawingswherein like numerals are be such as to prepare them to withstand thisinemployed to designate like parts throughout the tense heat. same, I Animportant object of the invention is the pro- Fig. l is a plan view of atunnel kiln constructed l5 vision of an improved construction of tunnelkiln in accordance with the present invention, wherein the firing of thepots or other articles Fig. 2 is a transverse section taken substanbeingtreated will be achieved in a thorough and tially on line 2-2 of Fig. 1,efiicient manner and also wherein the said pots Fig. 3 is a transversesection through one of or other articles may be gradually brought to thethe combustion chambers showing the heating g0 desired maximumtemperature without danger means therefor, of breaking, cracking, orweakening the same. Fig. 4 is a transverse section of the means forAnother object of the invention is the provision supplying air to thecombustion chambers, of an improved tunnel kiln construction compris-Fig. 5 is a transverse section taken substantially 5 ing a primarytunnel structure wherein the maxion line 5-5 of Fig. 1, i mum firingtemperatures are attained and a Fig. 6 is a side elevation of a portionof the preheating tunnel structure through which the primary tunnelstructure, pots or other articles being treated are first Fig. 7 is atransverse section taken substanpassed and gradually raised to a desiredpretially on line '|--'l of Fig. 1, and determined temperature prior tobeing introduced Fig. 8 is a longitudinal section taken substan- 3 intothe primary tunnel structure. tially on line 8-8 of Fig. 1. Anotherobject of the invention is the provision Referring now to the drawingsand particuof an improved tunnel kiln construction of the larly to Fig.1, the letter A designates in its above character wherein the primarytunnel entirety the primary tunnel structure wherein the structureincludes a high temperature or firing maximum firing temperatures areattained and 35 zone and an auxiliary heating zone through B thepreheating tunnel structure wherein the which the pots or other articlespass before enpots or other articles being treated are first tering thesaid firing zone, together with means gradually brought to a desiredpredetermined for heating said firing zone, and means for utitemperaturebefore being introduced into the 40 lizing a portion of such heat toassist in heating primary tunnel structure. 40 the auxiliary heatingzone. The primary tunnel structure A and preheat- Another object of theinvention is to provide, ing tunnel structure B are arranged side byside in a tunnel kiln of the above character, a prein parallel relationrelative to one another with heating tunnel structure of novel andimproved the exit end of the preheating tunnel structure 5 constructionwherein the pots or other articles being disposed substantially oppositethe intake may be gradually brought to a desired predeterend of theprimary tunnel structure, to the end mined temperature in an efficientand economical that the pots or other articles can be readily and mannerprior to being transferred into the priquickly transferred from theformer into the latmary tunnel structure. ter without any undue loss ofheat and without A further object of the invention is to provide beingadversely affected by atmospheric condi- 50 a tunnel kiln of the abovecharacter embodying tions during the transfer. so-called track coolingmeans located in the high As brought out above, the improved tunnel kilntemperature or firing zone of the primary tunnel herein provided hasbeen primarily designed for structure and wherein means is employed foruse in the firing of refractory glass melting pots receiving heated airfrom thesaid track cooling and will therefore be described and likewiseillustrated in the drawings in this connection, although it is to beremembered that it may be also employed with equally satisfactoryresults in the treatment of other articles.

The pots to be fired are adapted to be carried first through thepreheating tunnel structure B and thence through the primary tunnelstructure A upon a series of traveling cars or trucks; One of thesepots, designated by the numeral I0, is shown at the right in Fig. 1 inposition to be introduced into the intake end of the preheating tunnelstructure B, said pot being carried by a work car or truck H which isadapted to travel along rails I2 extending longitudinally through thetunnel structure. The pot is supported above the top of the Work carupon a plurality of refractory blocks l3 to permit of the circulation ofheated air beneath said pot. The work cars are mounted upon wheels [4carried by axles l5 and which are adapted to run along the said railslg.

The primary tunnel structure A is divided or separated into a hightemperature or firing zone a and an auxiliary heating zone 27, the potsafter being passed through the preheating tunnel structure B beingintroduced into and caused to pass first through the auxiliary heatingzone I) of the primary tunnel structure and thence through the hightemperature or firing zone a thereof wherein the maximum heatingtemperatures are attained. Extending longitudinally through the primarytunnel structure A are the spaced rails l6 upon which the work carstravel.

The pots are adapted to be moved intermittently through the preheatingtunnel structure and likewise through the primary tunnel structure, theintroduction of one work car into either tunnel structure causing all ofthe preceding cars therein to be moved forwardly the length of one car,with the last car being discharged from the exit end of the respectivetunnel structure.

Any suitable means may be provided for charging the cars or trucks I linto the preheating tunnel structure B. One such means, illustrated byway of example in Fig. 1, comprises a cable I! wound at one end about adrum l8 and provided at its free end with a hook l9 adapted to engagethe car II as the cable is wound upon the drum and to pull the said carinto the kiln, said cable being trained about suitable pulleys, onebeing shown at 23. The drum #8 may be driven by means of a chain andsprocket drive or the like 2| to effect the winding of the cablethereupon.

In order to effect the transfer of the work cars H from the outlet endof the preheating tunnel structure B to the intake end of the primarytunnel structure A, there is provided the transversely extendingtransfer track 22 upon which is mounted a transfer table 23, said tablecarrying rails 24 which are adapted to line up with the rails l2 and I6which extend longitudinally through the preheating and primary tunnelstruc tures respectively.

In practice, the introduction of one work car into the preheating tunnelstructure will cause all of the preceding cars therein to be movedforwardly the length of one car, with the last car being discharged fromthe tunnel structure onto the transfer table 23, it being understoodthat the said transfer table has been previously moved into positionwhere the rails 24 thereon are in alignment with the rails l2. Thetransfer table is then moved transversely along track 22 to bring thework car and pot into a substantially square receiving chamber 25 whichmay be located at the forward end of the primary tunnel structure. Therails 24 are brought into alignment with rails l6 whereupon the carcarrying the pot can be moved from the transfer table into and throughthe primary tunnel structure. Any suitable means can be provided forcharging the work cars into the primary tunnel structure. Likewise, ifdesired, the receiving chamber 25 may be omitted and the transfer tablemoved directly into the forward end of the auxiliary heating zone b.

With reference particularly to Fig. 2, the main heating zone a of theprimary tunnel structure A comprises opposite side walls 25 and 27 and acrown 28 forming a horizontal tunnel chamber 29 through which the potsIll are carried. The bottom 30 of the tunnel chamber is built up ateither side of the kiln to provide the longitudinally extending ledgesor platforms 3! and 32 upon which are mounted the closed combustionchambers 33 and 34 respectively, said chambers being disposed atopposite sides of the pots l3 and extending longitudinally substantiallythe entire length of the chamber 29.

The combustion chambers 33 and 34 are elongated hollow structures havingwalls of fire clay, carborundum, or analogous refractory material. Themeans provided for heating each combustion chamber includes gas burners35 and 35, the burner 35 being located at the end of the combustionchamber adjacent the outlet end of the tunnel structure A, while theburner 35 is projected transversely into the combustion chamber at apoint in advance of the burner 35 and through the side wall 26.

The flames from the burners are adapted to travel longitudinally throughthe combustion chambers in a direction opposite to the direction oftravel of the pots, with the products of combustion passing from thesaid combustion chambers 33 and 34 through outlets 31 and 38 intoconduits 39 and 4e respectively, said conduits extending longitudinallyof the tunnel structure A and communicating at one end with a transversepipe 4| projecting exteriorly of the tunnel structure and havingconnected thereto a pipe 42 leading to a stack 43 through which thewaste gases may be exhausted to the atmosphere. Since the heating flamespass longitudinally through the combustion chambers from the outlet-endof the main heating zone a to the inlet end thereof, it will be seenthat the temperature in this zone will increase gradually from the inletend to the outlet end thereof.

The auxiliary heating zone b of the primary tunnel structure isrelatively narrower than the main heating zone a and comprises spacedvertical side walls 44 and 45 and a fiat top 56 (Fig. 5) defining atunnel chamber 41 in alignment with tunnel chamber 29, the side walls ofsaid auxiliary heating zone being of suitable refractory material andthe top thereof of metalor asbestos.

In accordance with the present invention, a portion of the heated airwithin the main heating zone a is adapted to be utilized to assist inheating the auxiliary heating zone b, and to this end there may beprovided a conduit 48 communicating with the tunnel chamber 29 adjacentthe inlet end thereof through the crown or arch 28, as best shown inFigs. 1 and 6. The heated air is withdrawn from said chamber by a pump49 driven from a motor .58 and is then forced by said pump through aconduit 5| terminating in vertical branch pipes 52 and 53 respectively,communicating with horizontal pipes 54 and 55 extending longitudinallyof the auxiliary heating zone at opposite sides thereof and from whichlead outlets or lines 56 and 51 entering the tunnel chamber 41 adjacentthe bottomthere'of and beneath the pots Hl. Associated with the fiues 56and 51 are dampers 58 and 59 respectively for regulating the heated airpassing into the auxiliary heating zone, while the amount of heated airwithdrawn from the main heating zone through the conduit 48 may becontrolled by a damper 6D. 7

By introducing the heated air into the auxiliary heating zone adjacentthebottom thereof and beneath the pots i0, thesaid air will be caused tocirculate upwardly around the pots and in this way effect a more uniformheating thereof. Likewise, the feeding of the heated air into the tunnelchamber 41 adjacent the bottom thereof will result in a more eventemperature condition therein from top to bottom thereof since theintroduction of the air in this manner will cause a forced circulationwithin the tunnel chamber and minimize any tendency towardStratification of the heated air. In order to prevent overheating of therails l6 within the main heating zone a and also to prevent overheatingof the running gear or the work cars ll, there are arranged at oppositesides of the path of travel of said cars a plurality of horizontallongitudinally extending pipes GI and 62 respectively through which airis adapted to be circulated under pressure to effect the desired coolingof the said rails and running gear. These pipes are commonly termedtrack cooling means and it has been customary in the past to simplydischarge the heated air from the pipes to the atmosphere, making no usethereof. The present invention, however, contemplates the utilization ofthe-heated air within the track cooling pipes to assist in heating theauxiliary heating zone I). To this end, the pipes 6i and 62 eachcommunicate at one end with a header 63 and connected with these headersis a pipe 64 extending transverselyof the tunnel structure andcommunicating at one end with a conduit 65 extending longitudinally ofsaid tunnel structure toward the inlet end thereof, the air being drawnthrough said conduit by a pump 66 operated by motor 61. Leading frompump 66 is a conduit 68 terminating in two substantially vertical branchpipes 69 and it which communicate with the horizontally disposed pipes Hand 12 arranged at opposite sides of the auxiliary heating zoneforwardlyof and being similar to pipes 54 and 55. Each of the horizontalpipes H and 12 has associated therewith a plurality of outlets or fiues13 which communicate with the tunnel chamber 41 adjacent the bottomthereof and beneath pots Ill. Each of the fiues I3 is provided with adamper M to regulate the heated air passing therethrough into the tunnelchamber.

The amount of heated air drawn through the conduit 65 by pump 66 may becontrolled-by a damper 15 with the undesired or surplus air beingshunted to the stack 33 throughthe pipe connection Tl between conduits42 and '65, said pipe TI having associated therewith a damper 'lii.Thus, by completely closing damper "l5 and opening damper l5, it will bereadily apparent that all of the heated air passing through conduit 65will be directed through pipe ii to stack 43, whereas upon closing ofdamper 16 and opening damper 15, the heated air will pass to theauxiliary heating zone. Any desired intermediate adjustment: of

the dampers l5 and 16 can of course be provided, depending upon theamount of heated air required.

It may be found desirable at times to supplement the heated air beingdrawn into the auxiliary heating zone through the conduit 65 and inorder to provide for this additional heat, a pipe connection '88 isprovided between the conduits 48 and 65 and within which connection isarranged a damper l9. By either partially or entirely opening thisdamper, a certain amount of heated air being drawn through conduit 68will pass through pipe '18 into conduit 65 and thence to the auxiliaryheating zone.

- The heated air taken from the track cooling pipes el and 62 andintroduced into the auxiliary heating zone I) will tend to flowrearwardly through the primary tunnel structure in the direction oftravel of the pots therethrough and constitutes the air supply for thegas burners 35 and 36. In other words, this air is utilized to supportcombustion of the flames from said burners. With the above in mind, eachcombustion chamber 33 and 3 5 terminates slightly short of the outer orrear end wall of the primary tunnel structure and disposed between thesaid combustion chamber and wall, in alignment with the former, is achambered block Mil (Fig. 4) having a chamber HI therein and an openingI l2 at the top thereof controlled by a slidable damper l i3. afterpassing longitudinally through the tunnel structure, will pass throughopening H2 into chamber l l i, as indicated by the arrows in Fig. 4 andthence longitudinally into the respective combustion chamber. a

The preheating tunnel structure B, which is relatively shorter than theprimary tunnel structure A, comprises spaced vertical side walls 88 andBi and a flat roof 32 cooperating toform a tunnel chamber 83 (Fig. '7),the side walls being of a suitable refractory material and the roofpreferably of corrugated metal or asbestos carried upon a series ofspaced transverse I-beams 8d.

The preheating tunnel structure is adapted to be heated by thecirculation of heated air longitudinally therethrough, this air beingintroduced into the tunnel chamber 83 adjacent the exit end thereof andwithdrawn from the said chamber adjacent'its inlet end so that thetemperature within the tunnel chamber will increase gradually from theinlet end to the outlet end thereof to cause a gradual heating up of thepots as they are carried therethrough. The heating means comprises aheating unit at including a plurality of steam coils 85 arranged withina casing 86, air being blown through the casing and around the steamcoils by the action of a fan or the like Bl driven from motor 88. As theair contacts the steam coils 85, it will of course be heated up, theheated air passing from casing 86 through a conduit 85; into thesubstantially vertical branch pipes 99 and iii which communicate withthe horizontal pipes 92 and 93 respectively arranged at opposite sidesof the preheating tunnel structure and extending longitudinally thereof.The pipes 92 and 93 are provided with a plurality-of outlets or flues 94and 95 respectively which communicate with the tunnel chamber 83preferably closely adjacent the bottom thereof and beneath pots l8.Arranged within each horizontal pipe 92 and 83 is a damper 95 forcontrolling the heated air passing therethrough and which may bemanually operable by a lever 97. 4

Apparatus substantially similar to that de- The heated air,

scribed above for introducing the heated air into the tunnel chamber 83may be provided for withdrawing the air from said chamber adjacent theopposite end thereof. Thus, there may be arranged at opposite sides ofthe preheating tunnel structure B, adjacent the inlet end thereof, thetwo. longitudinally extending pipes 98. and 9,9. in communication withthe tunnel chamber adjacent the bottom thereof through a plurality ofhorizontally spaced outlets or fiues I00 and HH.

respectively, each having associated therewith a,

damper (not shown) to regulate the rate of withdrawal of the air fromsaid chamber. Leading from the pipes 98 and 99 are the vertical conduitsI02 and i513 respectively communicating with a common conduit i9 3running to a stack [85.

While it is preferred to withdraw the heated air from adjacent thebottom of the tunnel chamber, it may under some conditions be removedfrom the top thereof by extending the conduit I04 as at I96 andprojecting it through the roof 82 of the preheating tunnel structure.Associated with the extension M16 is a damper I0! controlled by a leverI63, while associated with each vertical conduit I02 and I 63 is adamper I09. By properly regulating the dampers I88 and I09, the heatedair can be withdrawn in proper amounts either from the top of the tunnelchamber or from adjacent the bottom thereof.

The introduction of the heated air into the tunnel chamber t3 adjacentthe bottom thereof and likewise the removal of the air from said chamberalso adjacent the bottom thereof constitutes a very desirable andimportant feature of the present invention in that this particulararrangement lends itself to the maintenance of a much more even anduniform temperature condition within the preheating tunnel structurefrom the bottom to the top thereof. Thus, the introduction of the heatedair into the tunnel chamber adjacent the bottom thereof results in aforced circulation of the air therein and reducing stratification of theheated air to a minimum. Likewise, the removal of the air from adjacentthe bottom of the tunnel chamber results in the heated air, whichnormally rises to the top of the chamber, being drawn downwardly aroundthe pots. Consequently, the pots will be evenly and uniformly heated asthey are carried through the preheating tunnel chamber.

As pointed out above, in the operation of the improved tunnel kilnherein provided, the pots IE to be treated are first passed through thepreheating tunnel structure B and thence through the primary tunnelstructure A, with the maximum firing temperatures being attained in themain heating zone a. of the latter tunnel structure. Although thisinvention is of course not restricted to the use of any specifictemperatures within different portions or zones of the tunnel kiln, yetit might be stated, by way of example only, that the temperature at theinlet end of the preheating tunnel structure may be in the neighborhoodof 125 to 150 degrees Fahrenheit when firing glass melting pots, withthe temperature at the outlet end thereof being approximately 300 to 350degrees Fahrenheit. The temperature at the intake end of the primarytunnel structure A is preferably substantially the same as thetemperature at the exit end of the preheating tunnel structure B, sothat the pots will not be subjected to any great difference intemperature upon being transferred, from the latter into the former. Thepots, upon, being passed, through the primary tunnel, structuraaregradually increased in temperature and the tem perature at, the exit endof said primary tunnel structure may be in the neighborhood of from 1925to 1975 degrees Fahrenheit.

.When the pots are removed from the kiln, they are adapted to be placeddirectly within a socalled pot furnace and to have molten glassproducedtherein, By the use of the apparatus herein provided, the potscan be gradually brought to the desired maximum temperature evenly anduniformly without danger of breaking, cracking, or weakening thev sameand so that they will be able to withstand the intense heat to whichthey are subjected during the melting of the glass therein. The potsmust. not only be heated to a high temperature but must also bethoroughly dried during the heating up thereof. Glass melting potsordinarily contain a. relatively large percentage of moisture and thismoisture must be gradually removed without in any way adverselyaffecting the pots. For instance, a pot weigh ing approximately 2500pounds will contain anywhere from 1% to 2% of moisture, meaning that thepot will contain 25 to 50 pounds of water which must be-removed duringthe firing operation. The tunnel kiln herein provided will acttothoroughly dry and fire the pots in an efficient and practical manner.Also, the use of heated air from the main heating zone a and. likewisefrom the track cooling means to effect the desired, heating of theauxiliary heating zone I; will tend to reduce fuel costs to a minimum.

It is to be understood that the form of the invention herewith shown anddescribed is to be taken as the preferred embodiment of the same, andthat various changes in the shape, size and arrangement of parts may beresorted to without departing from the spirit of the invention or thescope, of the subjoined claims.

We claim:

1. In a tunnel kiln construction, a tunnel structure including a mainheating zone and an auxiliary heating zone in substantial alignment withone another, means for carrying the work to be treated through saidzones, means for heatingthe main heating zone, and means for receiving.a. portion. of. the heat from said main heating zone and introducing itinto opposite sides of the auxiliary heating zone adjacent. the bottomthereof.

2. In a tunnel kiln construction, a. tunnel structure including a mainheating zone and an auxiliary heating. zone in substantial alignmentwith one another, tracks extending longitudinally through-said zones,work cars movable along said, tracks and adapted to carry the work tobetreated, track cooling means including a plurality of pipes extendinglongitudinally of the main heating zone and? through which air'underpressure is adapted to be passed; and means. for receiving'the heated;air from said pipes andintroducing it into said auxiliary heating zoneto assist in heating the latter.

3. In a tunnelv kiln. construction, a tunnel structure including a mainheating zone and an auxiliary heating zone in substantial alignment withone anothentracks extending longitudinally through said zones, work carsmovable along said tracks and adapted to carry the work to be treated,track cooling means including a plurality of pipcsextendinglongitudinally of the main heating zone and through which air underpressure is adapted to be passed, and means for receiving the heated airfrom said pipes and introducing it-into opposite sides of the auxiliaryh ap for receiving the heated introducing it into opposite sides of theauxiliary said main heating zone ing zone adjacent the bottom thereofand beneath said work.

' 4. In a tunnel kiln construction, a tunnel structure including a mainheating zone and an auxiliary heating zone in substantial alignment withone another, tracks extending longitudinally through said zones, workcarsmovable along said tracks and adapted to carry the work to betreated, means for heating the main heating zone, means for receiving aportion of the heat from said main heating zone and introducing it intosaid auxiliary heating zone to assist in heatzone to also assist in theheating thereof.

5. In a tunnel kiln construction, a tunnel structure including a mainheating zone and an auxiliary heating zone in substantial alignment withone another, tracks extending longitudinally through said zones, workcars movable along said tracks and adapted to carry the work to betreated, means for heating the main heating zone, means for receiving aportion of the heat from said main heating zone and introducing it intosaid auxiliary heating zone to assist in heating the latter, trackcooling means including a pluralityrof pipes extending longitudinally ofthe main heating zone and through which air under pressure is adapted'to be passed, and means air from said pipes and heating zone adjacentthe bottom thereof and beneath said work to also assist in the heatingof the latter.

6. In a tunnel kiln construction, atunnel structureincluding a mainheating zone and an auxiliary heating zone in substantial alignment withone another, tracks extending longitudinally through said zones, workcars movable along said tracks and adapted to carry the work to betreated, means for heating the, main heating zone, means for receiving aportion of the heat from said main heating zone and introducing it intoopposite sides of the auxiliary heating zone adjacent the bottom thereofand beneath said work to assist in heating the latter, track coolingmeans including a plurality of pipes extending longitudinally of themain heating zone and through which air under pressure is adapted to bepassed, and means for receiving the heated air from said pipes andintroducing it into said auxiliary heating zone to also assist inheating the latter.

7. In a tunnel kiln construction, a tunnel structure including a mainheating zone and an auxiliary heating zone in substantial alignment withone another, tracks extending longitudinally through said zones, 'workcars movable along said 'tracks and adapted to carry the work to betreatthe main heating zone, portion of the heat from and introducing itinto opposite sides of the auxiliary heating'zoneadjacent the bottomthereof and beneath said Work to assist in heating the latter, trackcooling means including a plurality of pipes extending longitudinally ofthe main heating zone and through which air under pressure is adapted tobe passed, and means for receiving the heated air from said pipes andintroducing it into opposite sides of the auxiliary heating zoneadjacent the ed, means for heating means for receiving a bottomthereofand beneath said work to also assist in heating the latter.

8. In a tunnel kiln construction, a tunnel structure including sidewalls and a top cooperating to define a longitudinally extending tunnelchamber, means for carrying the work to be treated through said chamber,means for introducing heated air into opposite sides of the chamberadjacent the bottom thereof beneath said work and also adjacent its exitend, and means for withdrawing the air from said chamber adjacent theinlet end thereof.

9. In a tunnel kiln construction, a tunnel structure including sidewalls anda top cooperating to define a longitudinally extending tunnelchamber, means for carrying the work to be treated through said chamber,means for introducing heated air into the chamber adjacent the exit endthereof, and means for withdrawing the air from opposite sides of thechamber adjacent the bottom thereof beneath said work and also adjacentits inlet end.

10. In a tunnel kiln construction, a tunnel structure including sidewalls and a top cooperating to define a longitudinally extending tunnelchamber, means for carrying the work to be treated through said chamber,means for introducing heated air into opposite sides of the chamberadjacent the bottom thereof beneath said work and also adjacent its exitend, and means for withdrawing the air from opposite sides of thechamber also adjacent the bottom thereof beneath said work and adjacentits inlet end.

ll. In a tunnel kiln construction, a primary tunnel structure and apreheating tunnel structure arranged alongside one another, with theoutlet end of said preheating tunnel being disposed substantiallyopposite the inlet end of said primary tunnel structure, means forcarrying the Work to be treated through said tunnel structures, saidprimary tunnel structure including a main heating zone and an auxiliaryheating zone, meansfor heating the main heating zone, means forreceiving a portion of the heat from said main heating zone and feedingit into said auxiliary heating zone to assist in heating the latter, andseparate means for heating the preheating tunnel structure. 7

12. In a tunnel kiln construction, a primary tunnel structure and apreheating tunnel structure arranged alongside one another, with theoutlet end of said preheating tunnel being disposed substantiallyopposite the inlet end of said primary tunnel structure, means forcarrying the work to be treated through said tunnel structures, saidprimary tunnel structure including a main heating zone and an auxiliaryheating zone, means for heating the main heating,zone,.means forreceiving a portion of the heat from said main heating zone and feedingit into opposite tunnel structure and a preheating tunnel structurearranged alongside one another, with the outlet end of said preheatingtunnel structure being disposed substantially opposite the inlet end ofsaid primary tunnel structure, means for carrying the work to be treatedthrough said tunnel structures, means for heating the primary tunnelstructure, means independent of said heating means for introducingheated air into opposite sides of the preheating tunnel structureadjacent the bottom thereof beneath said work and also adjacent its exitend, and means for withdrawing the air from opposite sides of the saidpreheating tunnel structure also adjacent the bottom thereof beneathsaid work and adjacent its inlet end.

, 15. In a .tunnel kiln construction, a primary tunnel structure and apreheating tunnel structure arranged alongside one another, with theoutlet end of said preheating tunnel being disposed substantiallyopposite the inlet end of said primary tunnel structure, means forcarrying the work to be treated through said tunnel structures, saidprimary tunnel structure including a main heating zone and an auxiliaryheating zone, means for heating the main heating zone, means forreceiving a portion of the heat from said main heating zone and feedingit into said auxiliary heating zone to assist in heating the latter,means independent of said heating means for introducing heated air intothe preheating tunnel structure adjacent the outlet end thereof, andmeans for withdrawing the air from said preheating tunnel structureadjacent the inlet end thereof.

.16. In a tunnel kiln construction, a primary tunnel structure and apreheating tunnel structure arranged alongside one another, with the:outlet end of said preheating tunnel being disposed substantiallyopposite the inlet end of said primary tunnel structure, means forcarrying the work to be treated through said tunnel structures, saidprimary tunnel structure including a main heating zone and an auxiliaryheating zone, means for heating the main heating zone, means forreceiving a portion of the heat from said main heating zone andintroducing it into opposite sides of the auxiliary heating zoneadjacent the bottom thereof beneath said work to assist in heating thelatter, means independent of said heating means for introducing heatedair into oposite sides of the preheating tunnel structure adjacent thebottom thereof and also adjacent its exit end, and means for withdrawingthe airfrom opposite sides of said preheating tunnel structure alsoadjacent the bottom thereof beneath said work and adjacent its inletend.

17. In a tunnel kiln construction, a tunnel structure including a mainheating zone and an auxiliary heating zone in substantial alignment withone another, tracks extending longitudinally through said zones, workcars movable along said tracks and adapted to carry the work to betreated, closed combustion chambers extending longitudinally of the mainheating zone at opposite sides thereof, gas burners for introducingflames into the combustion chambers adjacent the outlet end of the mainheating zone, a stack,

means for receiving the products of combustion from said combustionchambers and delivering them to said stack, track cooling meansincluding a plurality of pipes extending longitudinally of the mainheating zone and through which air under pressure is adapted to bepassed, means for receiving the heated air from said pipes andintroducing it into the said auxiliary heating zone to assist in theheating thereof, and damper controlled connections between saidlast-mentioned means and stack whereby a portion of the'heated air fromthe track cooling means may be passed to the stack if and when desired.

18. In a tunnel kiln construction, a tunnel .means for receiving aportion of the heat from said heating zone and introducing it into saidauxiliary heating zone to assist in heating the latter, track coolingmeans including a plurality of pipes extending longitudinally of themain heating zone and through which air under pressure is adapted to bepassed, means for receiving the heated air from said pipesandintroducing it into said auxiliary heating zone to also assist in theheating of the latter, and damper controlled connections between themeans for receiving a portion of the heat from said main heating zoneand the means for receiving the heated air from said pipesso that aformer may be passed to the latter if and when desired. 7

19. In a tunnel kiln construction, a tunnel structure including a mainheating zone and an auxiliary heating zone in substantial alignment withone another, tracks extending longitudinally through said zones, workcars movable along said tracks and adapted to carry the work to betreated, closed combustion chambers extending longitudinally of the mainheating zone at opposite sides thereof, gas burners for introducingflames into the combustion chambers adjacent the outlet end of the mainheating zone, a stack, means for receiving the products of combustionfrom said combustion chambers and delivering them to said stack, meansfor receiving a portion of the heat from said main heating zone andintroducing it into the auxiliary heating zone to assist in heating thelatter, track cooling means including a plurality of pipes extendinglongitudinally of the main heating zone and through which air underpressure is adapted to be passed,

means for receiving the heated air from said pipes and introducing itinto the auxiliary heating zone to also assist in heating the latter,damper controlled connections between said lastmentioned means and stackwhereby a portion of the heated air from the track cooling means maybe'passed to the stack if and when desired, and dampercontrolled-connections between the means for receiving a portion of theheat from the main heating zone and the means for receiving the heated'airfrom said pipes whereby heat may be passed from the former to thelatter if and when desired.

JOHN J. SCHARF. WILLIAM vI-IASSELBACH. LUTHER T. STROMMER.

portion of the heat from the

